Question: $ { \left[\begin{array}{r}{1} \\ {-1} \\ {3}\end{array}\right]+\left[\begin{array}{r}{3} \\ {1} \\ {1}\end{array}\right] = {?} } $
Explanation: To find the sum of two matrices, add the corresponding items between each matrix. ${\left[\begin{array}{r}{1}+{3} \\ {-1}+{1} \\ {3}+{1}\end{array}\right]}$ Now, simplify: ${\left[\begin{array}{r}{4} \\ {0} \\ {4}\end{array}\right]}$